Biochar Process and Apparatus

ABSTRACT

A pyrolysis apparatus for processing carbon rich precursor feedstock into carbon rich biochar and associated carbon rich by-products includes a combustion chamber for high temperature low oxidative combustion of the feedstock having an inlet for the feedstock at a first end and outlet for the biochar at a second end; a heater to heat the combustion chamber; at least one gaseous outlet positioned between the first and second ends and communicating with an interior of the chamber, each of the gaseous outlets provided with an air venturi to control extraction of pyrolysis gas generated within the combustion chamber.

INTRODUCTION TO THE INVENTION

This invention relates to the production of biochar and related carbon rich by-products using pyrolysis and in particular to an improved apparatus and methods allowing for the passive use and control of pyroligneous gasses within a continuous feed pyrolysis system.

BACKGROUND OF THE INVENTION

The pyrolysis process has been used for thousands of years for the production of charcoal from organic material, principally timber. From these early times, through to the present, the main purpose of producing charcoal was for its value as a fuel. Now in the 21^(st) century, charcoal production has received a great deal of interest for its properties as a soil amendment, and as a means with which to sequester atmospheric carbon (CO2) in the soil. Additionally, the process produces more energy, in the form of a synthesis gas (syngas), than it consumes, this aspect is increasingly being looked upon as a means to generate renewable energy. Charcoal manufactured for its agricultural and climate ameliorant properties is now called “Biochar.”

Current pyrolysis processes rely on the reactor chamber being equipped with mechanical or material seals to exclude atmospheric air from the chamber and require mechanically operated valves that are heavily insulated and/or heated via an external heat source to eliminate tar build-up, to manage and direct gas flow as it is generated from the process, for either combustion to maintain the reaction/process, or as a fuel source for energy production or other purposes. The abrasive nature of organic material and the entrained contaminates such as soil and gravel create problematic operational and wear issues for current sealing systems. The same can be said for the operation of valves to manage the pyrolysis gases. These gases have a high proportion of heavy tars, organic acids and fine particles of charcoal and ash, resulting in considerable wear and contaminant build-up on critical valve surfaces resulting in valve failure, or impeded operation.

A pyrolysis system utilising passive gas flow and maintaining a steady state within the pyrolysis combustion chamber would reduce or eliminate the need for mechanical seals to exclude atmospheric air from the chamber and therefore provide an improved simplified system of improved reliability.

SUMMARY OF THE INVENTION

In a first aspect the invention provides a pyrolysis apparatus for processing carbon rich precursor feedstock into carbon rich biochar and associated carbon rich by-products comprising:

a) a combustion chamber for high temperature low oxidative combustion of said feedstock having an inlet for said feedstock at a first end and outlet for said biochar at a second end;

b) heating means to heat said combustion chamber;

c) one or a plurality of gaseous outlets positioned between said first and second ends communicating with the interior of said chamber,

wherein said gaseous outlets are each provided with an air venturi to control the extraction of pyrolysis gas generated with said combustion chamber.

The combustion chamber may comprise a single or multiple reaction chambers.

In a particularly preferred embodiment the combustion chamber comprises a plurality of reaction chambers connected in series to provide a continuous flow wherein said plurality of gaseous outlets are individually fitted to each separate reaction chamber in said series.

In another aspect the invention provides a method for pyrolytic generation of biochar and associated pyroligneous gas products from carbon rich precursor feedstock comprising the following steps:

a) preheating a continuous flow pyroloysis combustion chamber having a first end and second end and having one or a plurality of reaction chambers connected in series to a desired start-up temperature using an external heating means;

b) feeding said precursor feedstock into a first end of said combustion chamber;

c) heating said combustion chamber with minimal oxidation;

d) extracting pyroligneous gasses from different positions within said combustion chamber between said first and second ends so as to draw off differing gas compounds and/or condensates generated at said different positions;

e) drawing biochar from said second end of said combustion chamber,

wherein said gas extraction is effected so as to maintain the internal pressure of said combustion chamber at or just below atmospheric pressure.

The gas extraction is preferably effected by a venturi action.

The air venturi, using a small amount of compressed air supplied by an air compressor (or other by other mechanical means), is used to create a low pressure zone to draw pyrolysis gases out of the reactor chamber or chambers within the pyrolysis unit. The air venturi is positioned to extract gases at different points, and temperatures, within the chamber/s. Multiple reactor chambers can be linked to form one continuous unit, providing multiple points with which to extract these gases which, being formed at different temperatures and having different residence times within the unit, contain and exhibit different properties. The extraction of these gases can be controlled so as to maintain the internal reactor pressure at, or just under, external atmospheric air pressure.

In a particularly preferred embodiment some of the pyrolysis gasses may be used as combustion gasses to heat the combustion chamber.

The air venturi system, may be positioned remotely from the actual pyrolysis chamber/s and are located immediately adjacent to the point at which these gases are either consumed as combustion gas with which to maintain the process, or at the point at which these gases are harvested.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the apparatus of the present invention;

FIG. 2 is a schematic representation showing details of the air venturi system of the present invention which is used to control the gaseous flow of syngas from the combustion chamber; and

FIG. 3 is a schematic representation showing the positioning of the venturi at the remote end of the gas transfer pipes and removed from the direct heat of the reaction chamber.

DETAILED DESCRIPTION OF THE INVENTION

The basis of the pyrolysis process is that of organic material of an animal or vegetable origin, being heated in an enclosed chamber resulting in a solid carbonaceous material (Biochar/Charcoal) and gaseous volatile compounds. The transformation from a solid or liquid state to that of a gas results in a vast increase in volume. And being in a sealed (or partially sealed) chamber, this equates to an increase in pressure over the external atmospheric conditions. The difference in pressure between the internal pyrolytic conditions and that of the external atmosphere, is dependent on how the generated gases are vented/extracted from the pyrolysis chamber.

One particularly preferred embodiment of the invention will now be described with respect to FIGS. 1 and 2.

FIG. 1 is a schematic representation of the apparatus of the invention in one particularly preferred form where the pyrolysis apparatus comprises a combustion chamber 1 in the form of an inclined cylindrical chamber to the angle of an inclination being approximately 20 degrees. The combustion chamber has an internal feed ablative screw adapted to rotate within the combustion chamber so as to assist in the continuous movement of the raw feedstock 2, which is fed through the inlet 3 of the combustion chamber 1, with the inlet positioned towards the first end 4 of the combustion chamber.

In order to initiate the pyrolysis reactions, the combustion chamber 1 is provided with a furnace 7 fed by a propane tank 10. The propane fired furnace is necessary in order to initiate the pyrolysis reaction within the combustion chamber 1. The reaction within the combustion chamber is assisted by the rotary movement of the ablative screw which assists in the distribution and movement of the raw feedstock up the combustion chamber 1, ensuring that the feedstock is uniformly heated and caused to contribute to the reaction within the combustion chamber. The pyrolysis reaction causes the production of various gasses at different stages and the apparatus of the invention provides a plurality of gaseous outlets 8, positioned along the length of the combustion chamber between the first end 4 and the second end 6 thereof.

The combustion chamber 1 is preferably made up of two reactors 9 placed in series such that the in series reactors 9 provide the combustion chamber 1 having a first end 4 and a second end 6. The end product of the pyrolysis process is biochar which is fed out by the continuous action of the ablative screw and caused to exit from the second end 6 at the biochar outlet 5.

The apparatus of the invention is particularly configured to maintain a passive steady state reaction within the combustion chamber whereby the pressure within the chamber is maintained substantially at atmospheric level by the passive drawing off of gaseous bi-products via the gaseous outlets 8 into gas transfer pipes 15. In this manner, the combustion chamber does not require highly engineered seals and valves in order to maintain internal pressures as internal pressures are largely avoided with the interior of the combustion chamber being maintained at or just under atmospheric pressure.

The control of the pyrolysis gas flows are preferably managed by air venturi systems rather than gate valves or the like. The maintenance of the combustion chamber at or just under atmospheric pressure allows the use of air venturi control systems and also allows for gas extraction at different and various points in the pyrolysis process thereby enabling pyroligneous gas compounds to be extracted at various stages along the combustion chamber and throughout the pyrolysis process so as to assist in the extraction of the gasses with their own separate and intrinsic properties rather than the drawing off a gaseous product as one homogenous mixture.

The venturi are preferably positioned at or near the end of the gas pipe remote from the heat of the reactor 9.

The temperature control valve 12 is air regulated controlled by a separate temperature controller, e.g. if the primary reactor 9 begins to heat up to a high temperature level, the temperature controller can reduce the air to the venturi directing syngas to the furnace and at the same time, increase the air to venturi directing syngas to the condensers. This reduces combustible syngas going to the furnace and thereby reduces the temperature and allows control of the temperature of the reactor using the products of combustion without the continued need for propane activation of the furnace 7.

FIG. 2 shows detail of the air venturi system used to control the gaseous flow of syngas from the combustion chamber.

The multiple air-venturi 13 are used to manage/control syngas (or producer gas) generated from the thermal decomposition of organic matter in a pyrolysis process.

The air-venturi units 13 are positioned for attachment at the remote end of the gaseous outlets such that application of compressed air via a compressor 14 allows the venturi to apply a vacuum to the gaseous outlet unit and hence draw gas from the reactor chamber without the need for valves or other physical gating systems.

The passive maintenance of the combustion chamber at or near atmospheric pressure and the combined use of the air-venturi system allows the said syngas to be exported simply and without the need for mechanical valves or other such apparatus from the pyrolysis process to various destinations; direct to the furnace for combustion for the purpose of maintaining the process at an optimum temperature, to one or more condenser for the purpose of removing condensable products that may have commercial value, and for combustion elsewhere for the purpose of generating energy/heat.

The air-venturi can be manually operated or system controlled to extract syngas at the same rate, or slightly greater rate, than it is being generated at in the pyrolysis process. This makes redundant the need for problematic mechanical valves and gas sealing systems required to contain said gases within a conventional pyrolysis system, because pressure within the system can be maintained at, or just below, that of atmospheric pressure.

The pressurised air, either from an air-compressor or positive displacement air-fan, that provides the motive force to drive an air-venturi, is metered at such a rate as to create an ideal fuel (syngas)/air mixture for optimum combustion/energy production.

FIG. 3 shows the positioning of the venturi 13 at the remote end of the gas transfer pipes 15 and removed from the direct heat of the reaction chamber or chambers.

The invention provides for the first time, a modified pyrolysis apparatus designed to work substantially at/or below atmospheric pressure thereby eliminating the need for high pressure valves and seals to control the generation of biochar and pyrolysis gasses. The steady state operation of the combustion chamber allows the more passive removal of pyroligneous gasses at selected points along the combustion chamber by the application of air venturi mechanisms such that the apparatus and methods of the invention provide a low-pressure maintenance free and highly reliable apparatus and methods for producing biochar and related carbon rich bi-products.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 

1. A pyrolysis apparatus for processing carbon rich precursor feedstock into carbon rich biochar and associated carbon rich by-products comprising: a) a combustion chamber for high temperature low oxidative combustion of said feedstock having an inlet for said feedstock at a first end and outlet for said biochar at a second end; b) a heater to heat said combustion chamber; c) at least one gaseous outlet positioned between said first and second ends and communicating with an interior of said chamber, each of said gaseous outlets provided with an air venturi to control extraction of pyrolysis gas generated within said combustion chamber.
 2. An apparatus according to claim 1 wherein said combustion chamber comprises multiple reaction chambers.
 3. An apparatus according to claim 1 wherein said combustion chamber comprises multiple reaction chambers connected together in series to provide continuous flow.
 4. An apparatus according to claim 1 wherein said combustion chamber comprises multiple reaction chambers connected together in series with each said gaseous outlets fitted to each separate reaction chamber in said series.
 5. A method for pyrolytic generation of biochar and associated pyroligneous gas products from carbon rich precursor feedstock, comprising the following steps: a) preheating a continuous flow pyrolysis combustion chamber having a first end and second end and having at least one reaction chamber connected in series to a desired start-up temperature using an external heater; b) feeding said precursor feedstock into said first end of said combustion chamber; c) heating said combustion chamber with minimal oxidation; d) extracting pyroligneous gasses from different positions within said combustion chamber between said first and second ends so as to draw off differing gas compounds and condensates generated at said different positions; e) drawing biochar from said second end of said combustion chamber; and f) effecting said gas extraction so as to maintain internal pressure of said combustion chamber at or just below atmospheric pressure.
 6. A method according to claim 5 further comprising the step of effecting said gas extraction by venturi action.
 7. A method according to claim 5 further comprising the step of using a portion of said extract pyroligneous gases as combination gases to heat a combustion engine. 